River
River is technically co-hostess, so of course she was there. She supports her wife!
If you run into her toward the start of the party, she's doing an excellent job of seeming at ease, but her ghostly little raccoon familiar is restless. Make of that what you will.
Still, she's friendly enough, and she'll greet people she knows or introduce herself to people she doesn't.
Catching her closer to the end of the party, she seems more genuinely relaxed and her spectral companion appears to finally agree. She'll still be willing to talk if spoken to, but she'll also be seeking out the Doctor at this point (as if she hasn't been quietly keeping tabs on her) to apologize for giving her a hard time about having this party in the first place.